1. Field of the Invention
The present invention relates to a voltage-reactive power control apparatus incorporated to reactive power supplying equipment for adequately sustaining load side voltages in the power system.
2. Description of the Prior Art
The voltage of a power system always fluctuates, as is well known, in accordance with change of demand and supply. Large voltage fluctuations affect not only normal application or operation life of a variety of electrical consumer appliances connected to the system, but also the insulation design of various power apparatus to be installed in the power system, and moreover interferes with stable and efficient operation of the system including a power generator from the viewpoint of operation of the power system. Namely, the voltage-reactive power control is essential for all electrical appliances and power apparatus connected to the power system to ensure normal operations and for realizing stable and efficient operation of the system.
Moreover, the increase in demand of power and difficulties in obtaining power plant sites caused by environmental concerns have resulted in power generation plants located in remote and localized, areas realization of large scale power generation base through utilization of a large capacity generator unit and long distance and high voltage transmission and heavier power flow in the power transmission facilities.
Of various problems to be overcome for safe and economical running of a higher density, larger capacity power system which is expanding and becoming more complicated year after year, following are considered as the essential problems, although a voltage problem may not easily be evaluated directly from the economical viewpoint in its effect.
(1) Voltage drop under a heavy load PA1 (2) Abnormal rise of voltage under light load PA1 (3) Voltage drop during system failure PA1 (4) Improvement in performance of voltage-reactive power control during system operation.
The items (1), (2) will be described hereunder in more detail.
In general, a voltage of power system is maintained and adjusted to a preset reference value through the voltage-reactive power control of the generator and phase modifying equipment. However, if the large supply power of VAR (volt-ampore Reactive) supply equipments falls as load increases suddenly or demand and supply of the reactive power is unbalanced, voltage of the primary system may abnormally fall or rise under the situation where the power system is large in scale.
Such a system operating situation is reported in detail in the Technical Report of Japan Electrical Engineering Society (Part II), No. 238, P60.
However, such voltage failure or unstable phenomenon is not eliminated. When a cause is once set up, a local and minor failure is first generated and it is then developed to the wider and major failure. Therefore, detection at early stage and quick countermeasures are required.
The voltage-reactive power control apparatus of the prior art has mainly assigned monitoring and operation for such voltage variation or voltage abnormalities to the load dispatching center which manages operation of the whole system. Moreover the information coming from the load end is delayed, and synchronized information is not obtained. Therefore this information is inaccurate and cannot be used.